1. Field of the Invention
The present invention relates to a process for fabricating a semiconductor laser emitting apparatus. More particularly, the present invention is concerned with a process for fabricating a semiconductor laser emitting apparatus which emits laser beams having two different wavelengths.
2. Description of the Related Art
A conventional process for fabricating a semiconductor laser emitting apparatus which emits laser beams having two different wavelengths is described below with reference to diagrammatic cross-sectional views of FIGS. 2A to 2H illustrating the fabrication process.
As shown in FIG. 2A, on an n-type substrate 110 comprised of GaAs, a first n-type buffer layer 131 comprised of GaAs, a first n-type cladding layer 132 comprised of AlGaAs, a first active layer (having a multiple quantum well (MQW) structure having an oscillation wavelength of 780 nm) 133, a first p-type cladding layer 134 comprised of AlGaAs, and a first p-type cap layer 135 comprised of GaAs are stacked on one another in this order by a metal organic vapor phase epitaxial growth (hereinafter, frequently referred to simply as xe2x80x9cMOVPExe2x80x9d) method.
Then, as shown in FIG. 2B, a resist film (not shown) is formed so that it covers a region 121 in which a first semiconductor laser emitting device is to be formed (first semiconductor laser emitting device formation region 121), and the layers of from the first p-type cap layer 135 to the first n-type cladding layer 132, excluding the portion corresponding to the first semiconductor laser emitting device formation region 121, are removed using the above resist film as-a mask by a wet etching process, such as a sulfuric acid system non-selective etching process and a hydrofluoric acid (HF) system selective etching process for AlGaAs, to thereby form, in the first semiconductor laser emitting device formation region 121, a first laminate 123 in which the first p-type cap layer 135, the first p-type cladding layer 134, the first active layer 133, and the first n-type cladding layer 132 are stacked on one another.
Subsequently, as shown in FIG. 2C, on the first n-type buffer layer 131, a second n-type buffer layer 136 comprised of InGaP, a second n-type cladding layer 137 comprised of AlGaInP, a second active layer (having a multiple quantum well (MQW) structure having an oscillation wavelength of 650 nm) 138, a second p-type cladding layer 139 comprised of AlGaInP, and a second p-type cap layer 140 comprised of GaAs are stacked on one another in this order by a MOVPE method so that they cover the first laminate 123.
Then, as shown in FIG. 2D, a resist film (not shown) is formed so that it covers a region 122 in which a second semiconductor laser emitting device is to be formed (second semiconductor laser emitting device formation region 122). The layers of from the second p-type cap layer 140 to the second n-type buffer layer 136, excluding the portion corresponding to the second semiconductor laser emitting device formation region 122, are removed using the above resist film as a mask by a wet etching process, such as a sulfuric acid system etching process for a cap layer and a phosphoric acid and hydrochloric acid system selective etching process for a quaternary-system compound semiconductor, and a hydrochloric acid system separation etching process, to thereby form, in the second semiconductor laser emitting device formation region 122, a second laminate 124 in which the second n-type buffer layer 136, the second n-type cladding layer 137, the second active layer 138, the second p-type cladding layer 139, and the second p-type cap layer 140 are stacked on one another. As a result, the first laminate 123 and the second laminate 124 are separated from each other.
Subsequently, as shown in FIG. 2E, insulating films 125 are formed on the first laminate 123 and the second laminate 124 so that they cover portions which are to be current injection regions, and then, for forming a stripe structure which is to be a current constriction structure of a gain guide type, from surfaces of the first p-type cap layer 135 and the second p-type cap layer 140 to halfway portions of the first p-type cladding layer 134 and the second p-type cladding layer 139 are respectively processed in a ridge form in a certain depth of the first p-type cladding layer 134 and the second p-type cladding layer 139 by an etching process using the insulating films 125 as a mask.
Then, as shown in FIG. 2F, an n-type layer 141 comprised of, for example, GaAs is allowed to selectively grow on the compound semiconductor layer, so that it implants the portions etched in a ridge form in the first p-type cladding layer 134 and the second p-type cladding layer 139.
Then, the insulating films 125 are removed by an etching process. Subsequently, as shown in FIG. 2G, a resist film (not shown) is formed so that it covers only the portions of the n-type layer 141 formed on the first laminate 123 and the second laminate 124, and then, the n-type layer 141 is removed by an etching process using the above resist film as a mask so that the only portions of the n-type layer 141 on the first laminate 123 and the second laminate 124 remain.
Then, as shown in FIG. 2H, the resist film is removed. Further, a first p-type electrode 143 and a second p-type electrode 144 respectively connected to the first p-type cap layer 135 and the second p-type cap layer 140 are formed from, for example, a Ti/Pt/Au laminate, and an n-type electrode 151 connected to the n-type substrate 110 is formed from, for example, a AuGe/Ni/Au laminate.
However, in the step for separating the first semiconductor laser emitting device comprising the first laminate from the second semiconductor laser emitting device comprising the second laminate, an exposure step for a resist film which serves as a mask for etching is inevitably performed in a state such that the surface step of the layer directly under the resist film is large. Therefore, it has been difficult to achieve the patterning for resist with precision.
In addition, it is necessary that the step for separating the first semiconductor laser emitting device comprising the first laminate from the second semiconductor laser emitting device comprising the second laminate by an etching process, and the step for separating the n-type layer which constitutes the current constriction layer by an etching process be separately conducted in two different separation steps. Therefore, a burden on the process has been large.
The present invention is a process for fabricating a semiconductor laser emitting apparatus which has been made for solving the above-mentioned problems accompanying the prior art.
The process of the present invention is a process for fabricating a semiconductor laser emitting apparatus comprising a first semiconductor laser emitting device and a second semiconductor laser emitting device, which are formed on a substrate and respectively oscillate laser beams having different wavelengths, the process comprising the steps of: stacking on the substrate a compound semiconductor layer which constitutes the first semiconductor laser emitting device, to thereby form a first laminate; removing the first laminate so that the portion of the first laminate in a region in which the first semiconductor laser emitting device is to be formed remains; stacking on the substrate a compound semiconductor layer which constitutes the second semiconductor laser emitting device, to thereby form a second laminate; removing the second laminate formed on the first laminate, to thereby expose a surface of the first laminate to the outside and planarize a surface of the second laminate; forming current injection regions in a ridge form in the first and second laminates, respectively; selectively forming a current constriction layer on the portion of the first and second laminates other than the current injection regions; and forming a space in the current constriction layer and between the first laminate and the second laminate, to thereby separate the first laminate from the second laminate.
The process for fabricating a semiconductor laser emitting apparatus of the present invention includes a step for removing the second laminate formed on the first laminate, to thereby expose the surface of the first laminate to the outside and planarize the surface of the second laminate. Therefore, in the subsequent step for separating the first laminate from the second laminate, to thereby form a space between the laminates, an exposure step for a resist film which serves as a mask for etching can be performed in a state such that the surface of the layer directly under the resist film is planarized, so that patterning for resist can be conducted with high precision, enabling the separation to be achieved with high precision.
In addition, in the process of the present invention, the step for separating the first laminate from the second laminate, to thereby form a space between the laminates, and the step for separating the current constriction layer by an etching process are conducted in the same separation step. Therefore, a burden on the process can be reduced.